[Haskell-beginners] Randomness, lists, and unfoldr

[Alex Rozenshteyn]

I'm trying to build a list where each entry depends on the previous one.
Unfoldr seemed like a good idea at the time.
Unfortunately, my values are monadic values (specifically RVars, from the
random-fu package).  Okay, shouldn't be a problem; I just monadic bind
and...

> -- example code
> updateCell :: Bool -> RVar Bool
> updateCell False = return False
> updateCell True  = bernoulli (0.9 :: Double)

> sim = sequence $ take 20 $ unfoldr (\x -> Just (x, x >>= updateCell))
(return True)

> runRVar sim DevURandom
[True,True,True,True,True,False,True,False,True,False,False,False,False,False,False,True,True,False,False,False]

That output shouldn't be possible if I'm doing things right...  It appears
that each cell has an independent history.  I'm stumped.
Advice on threading monad input in general and random-fu in specific would
be appreciated.

-- 
          Alex R
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